The theory runs like this. Usually cells die off in a controlled fashion—called apoptosis—which allows fresh cells to replace tired old ones. The process allows old malfunctioning cells to be destroyed before they go rogue and grow into tumors. But in order for our brains to grow bigger, our bodies have had to learn to extend the life of cells, delaying apoptosis and in turn increasing the risk of cancer development.

The new idea is published in PLoS One and isn't just grandiose academic posturing. In fact, it's backed up by an analysis of the lifecycle of cells from both humans, chimpanzees and macaques. The results point to the fact that human cells undergo apoptosis much more slowly—and are at greater risk of mutation as a result.

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Perhaps understandably, some academics warn that the theory should be taken with at least a small pinch of salt. "He has a sound experimental finding," explained Todd Preuss of the Yerkes National Primate Research Center in Atlanta, Georgia, to New Scientist. "What that means in the broader context is open to debate." Part of the problem is that there isn't really any systematic data on cancer rates in non-human primates to compare to.

Still, the idea is being taken seriously by many, and it could go a long way in explaining why cancer is such a serious medical problem for humans the world over. Let's just hope that cancer doesn't wipe us out before our brains are big enough to find a cure. [PLoS One via New Scientist]